Angina pectoris is a common symptom in both patients with and in those without obstruction to left ventricular outflow. The present study was designed to investigate coronary flow and myocardial hemodynamics and metabolism in such patients. Thirty-three HCM patients, 18 without obstruction and 15 with a greater than 30mmHg gradient in the left ventricular outflow tract, underwent study. We found that patients with obstructive hypertrophic cardiomyopathy had higher coronary flow and myocardial oxygen consumption at rest and during pacing compared to patients without obstruction, probably due to higher left ventricular systolic pressure and myocardial oxygen requirements. Flow was lower at the on set of ischemia in patients without obstruction, suggesting more limited peak flow capacity; this possible relates to left ventricular microvascular obstruction. The different coronary flow patterns between patients with and without obstruction further demonstrate that left ventricular outflow gradients produce important physiologic effects.